A Burning Candle

This experiment will introduce you to observations involving critical thinking plus use of your notebook to record observations before report writing and the type of reports desired in this laboratory.

Yogi Berra once said, "You can observe a lot by just watching." What he meant by this is that observation requires more than simply using your eyes . It also requires critical thinking during the observation process. You should be asking yourself questions about what you are seeing and why the behavior you are observing is taking place. That is, you should be formulating hypotheses and testing those hypotheses on a limited basis. This type of observation is extremely important in science since it provides the main method of acquiring data, detecting errors and unexpected occurrences, and achieving ultimate success in whatever component of science you are engaged in.

The key aspect of critical observation involves self-questioning. That is, you must learn to formulate questions based on what you are seeing that you can either answer immediately or attempt to answer at a later time. This type of question/answer dialogue, carried out internally, provides the mental aspect to the observation process which is so crucial in extending data acquisition to understanding and application. For example, when Alexander Fleming discovered penicillin in 1928, it was based on a critical observation involving mold growing on bread: some types of mold had areas surrounding them where no bacterial growth took place. This observation, in hindsight, appears trivial, but that is because we now understand the reason for the antibacterial activity; mainly that the mold produced penicillin which inhibited the growth of bacteria. Fleming's key discovery was based on a simple question: Why was no growth observed? and the important extension of the question to a hypothesis that could be tested using a scientific method. Such hypotheses eventually led to the discovery of penicillin and a revolution in modern medicine.

In this experiment you will make observations of a deceptively simple process: a burning candle. In fact, what takes place during the initiation and dynamically stable combustion process is enormously complex. There are insights into basic physics and chemistry which are important for you to be aware of and which can illustrate for you the importance of critical observations.

Procedure:

Take a match and light a candle. On the left side of your notebook (or if you not have a notebook yet, on a piece of notebook paper for later transcription) record all the observations you can make regarding the lighting and burning of the candle. Be aware that individual observations numbering over 100 have been recorded by others.

As you look at the candle, try to separate the components into the individual elements. The flame is different from the vapor which is different from the wick and the solid and liquid wax. There are processes in dynamic equilibrium occurring during the burning process. Think about these processes and ask yourself questions. There are physical changes occurring as well as chemical reactions: try to imagine what these are, list them, and ask questions about them. Your "observations" should also contain conjecture and hypotheses about what is occurring or why it is occurring. It is crucial that you have some of these extensions of the observation process recorded.

It may take you awhile to begin to think about what is happening. Be patient and work at the process. Once you begin to see how to ask questions related to what you are seeing, a snowball effect will occur that should open up whole new areas of observation for your critical consideration. Be sure to write down all of your thoughts and observations as they occur. Don't try to be critical of the material you write down, but simply put it down as quickly as possible. You will have plenty of opportunity later for evaluation and grouping of your data.

Polymer Flammability

Take part of a soft drink six-pack holder for flammabilitiy tests. Using your candle, bunsen burner, or a match, try to set the piece of flexible plastic on the fire over a suitable piece of disposable material such as a pie plate or paper plate. Observe the ignition and combustion process in the same way that you did for the candle. Look for phase changes, evidence of chemical reactions, physical processes, such as convection and condensation, and any other overall or detailed component of the behavior of the flame, the polymer, or interphase.

Choosing or designing polymers that are inherently non-flammable is one possible area where you could apply your observations and conclusions. Approaches we now use include all aromatic materials and polymers containing large amounts of phosphorous, silicon, or halogens. Alternatively, flame retardants may be added to the polymer composition that will inhibit flammability by one of two mechanisms. These materials are phosphorous esters, silicon and aluminum containing salts, and highly brominated or chlorinated aromatic or aliphatic additives.

The mechanism of flame-retardancy involves one of two overall approaches. The first is to completely prevent ignition. That is, the materials are inherently flame retardant and will not even catch fire. Many inorganic compounds are non-flammable. The second approach involves the release of radical scavengers such as halides. During the combustion process, decomposition of the polymer and the flame retardants occurs. However, the radical combustion process is inhibited or short-circuited by the presence of the halogen radicals which can act as terminating agents for chain reactions. This process takes place in the vapor phase just above the surface of the burning material.